Hooded crows solve a transitive inference problem cognitively

We investigated the ability of hooded crows to form transitive inferences. Subjects were trained to discriminate a series of overlapping pairs of stim uli: A+ B-, B+ C-, C+ D-, D+ E, where the letters stood for colour stimuli and plus and minus for rewarded or non-rewarded choices. The stimuli were c ards of different colours with a circle of the same colour on the reverse s ide and diameters decreased from A to E. To preclude an influence of the re inforcement history on choices with the test pair ED, art overcompensation phase was instituted after training If consisted of the presentation of all training pairs with frequencies selected so that the reward to non-reward ratios for stimulus D would be between 1.5 and 2.0 times greater than for B . If, during the ED test; the bird chose the stimuli according to these rat ios they should prefer D. If they chose according to diameter relation they should prefer B. During these tests, the crows strongly preferred B over D (83.1%). In a second experiment, subjects were trained with the same proce dure except that the diameters of the circles were all the same. During thi s test, the performance of two crows was not significantly, different from chance level (53.1%), and the other. two crows preferred D (80.0%). We conc lude that crows can solve transitivity tests using cognitive mechanisms if they are offered additional information (in this case circle diameter which , presumably, allows them to represent the relevant stimuli in an ordered s eries.